Method and digital circuit for generating a waveform from stored digital values

Abstract

In a particular embodiment, a method includes adjusting an input to a divider on a feedback path of a phase locked loop circuit based on a stored digital value representing a portion of a time-based waveform that is applied to a modulator circuit. The stored digital value is retrieved based on an output of the feedback path.

Description

I. FIELD[0001]The present disclosure is generally related to a method and digital circuit for generating a waveform from stored digital values.II. DESCRIPTION OF RELATED ART[0002]Advances in technology have resulted in smaller and more powerful computing devices. For example, there currently exist a variety of portable personal computing devices, including wireless computing devices, such as portable wireless telephones, personal digital assistants (PDAs), and paging devices that are small, lightweight, and easily carried by users. More specifically, portable wireless telephones, such as cellular telephones and Internet Protocol (IP) telephones, can communicate voice and data packets over wireless networks. Many such wireless telephones incorporate additional devices to provide enhanced functionality for end users for example, a wireless telephone can also include a digital still camera, a digital video camera, a digital recorder, and an audio file player. Also, such wireless teleph...

AI Technical Summary

Benefits of technology

[0004]A waveform generator having a memory for storing digital values may be used. The digital values are used by the waveform generator to construct a waveform. The waveform may take on a desired shape and may be changed or modified by storing new or modified digital values in the memory. The set of stored digital values may be overwritten, or the memory may allow multiple sets of digital values to be written, where each set represents a unique waveform. In the case of multiple sets of stored digital values, the particular set of stored digital values used to construct the waveform may be selected based on an index value, an identifier, or in some other manner. The waveform and a seed value are combined in a manner to spread the power density of an output clock over a particular frequency band. The signal-to-noise ratio (SNR) of the output clock may be improved by selecting a waveform, such as a sinusoidal waveform, that provides a faster roll-off of power density outside the particular frequency band.

[0007]One particular advantage provided by at least one of the disclosed embodiments is that a waveform with a desired shape to be applied to a modulator coupled to a frequency divider may be implemented by storing appropriate digital values in a memory. The waveform of the desired shape may be selected for improved performance characteristics of the PLL.

Problems solved by technology

However, the output clock signal that is generated by such circuits may have a large power density at a single frequency resulting in electromagnetic interference (EMI).

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